The Web2cToolkit is a frame-work for web-based control clients. Key elements are JAVA servlet and AJAX technologies. Applications based on the Web2cToolkit allow world-wide user access and provide user authentication and authorization. Typical use cases are overview panels, service panels for remote maintenance or user access to stored data for off-line analysis. The papers summarizes the conceptual design and presents example applications implemented for the PETRA3 project at DESY.